Methods for modifying multi-mode optical fiber manufacturing processes

ABSTRACT

Methods for modifying multi-mode optical fiber manufacturing processes are disclosed. In one embodiment, a method for modifying a process for manufacturing multi-mode optical fiber includes measuring at least one characteristic of a multi-mode optical fiber. The at least one characteristic is a modal bandwidth or a differential mode delay at one or more wavelengths. The method further includes determining a measured peak wavelength of the multi-mode optical fiber based on the measured characteristic, determining a difference between the target peak wavelength and the measured peak wavelength, and modifying the process for manufacturing multi-mode optical fiber based on the difference between the target peak wavelength and the measured peak wavelength.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority under 35 U.S.C. §119 ofU.S. Provisional Application Ser. No. 61/817,503 filed on Apr. 30, 2013which application is incorporated herein by reference.

BACKGROUND

1. Field

The present specification generally relates to optical fibermanufacturing processes and, more specifically, to methods for modifyingmulti-mode optical fiber manufacturing processes.

2. Technical Background

Manufacturing processes for producing multi-mode optical fiber typicallyinclude drawing multi-mode optical fiber from a glass perform that isheated in a draw furnace, cooling the drawn fiber, and coating the fiberafter it has sufficiently cooled. Multi-mode optical fiber is typicallyproduced to satisfy certain performance characteristics, such as for thedrawn optical fiber to possess a threshold bandwidth for light emittedat a particular wavelength. The process parameters employed by the fibermanufacturing process may have a significant impact on the resultantperformance characteristics of the drawn fiber. However, conventionalfiber manufacturing processes may not consistently produce fiber thatsatisfies desired performance characteristics, such as processes thatproduce fiber that does not satisfy quality control tests and cannot besold or must be sold as lower grade optical fiber.

Accordingly, a need exists for methods for modifying multi-mode opticalfiber manufacturing processes.

SUMMARY

Multi-mode optical fiber may be produced to satisfy a performancecharacteristic, such as a bandwidth, at a particular target peakwavelength. The inventors have discovered that the actual peakwavelength of a multi-mode optical fiber may influence the performancecharacteristics of the fiber. For example a difference between thetarget peak wavelength of the multi-mode optical fiber and the actualpeak wavelength (e.g., the measured or determined peak wavelength) of amulti-mode optical fiber may influence the bandwidth of the multi-modeoptical fiber at the target peak wavelength. Generally, as thedifference between the target peak wavelength and the actual peakwavelength increases, the bandwidth of the multi-mode optical fiber atthe target peak wavelength decreases. The inventors have recognized thatby measuring the actual peak wavelength of a multi-mode optical fiberand adjusting the fiber processing parameters, such as tension, in orderto decrease the difference (e.g., so that the actual peak wavelength ofsubsequently produced fiber will be closer to the target peakwavelength), performance characteristics of the produced optical fibermay be improved.

In one embodiment, a method for modifying a process for manufacturingmulti-mode optical fiber includes measuring at least one characteristicof a multi-mode optical fiber. The at least one characteristic is amodal bandwidth or a differential mode delay at one or more wavelengths.The method further includes determining a measured peak wavelength ofthe multi-mode optical fiber based on the measured characteristic,determining a difference between the target peak wavelength and themeasured peak wavelength, and modifying the process for manufacturingmulti-mode optical fiber based on the difference between the target peakwavelength and the measured peak wavelength.

In another embodiment, a method for adjusting at least one drawingprocess parameter in a process for manufacturing multi-mode opticalfiber includes coupling light emitted from at least one light source ata plurality of wavelengths into a multi-mode optical fiber, anddetermining a plurality of corresponding bandwidths for light emitted atthe plurality of wavelengths. Each wavelength is associated with acorresponding bandwidth. The method further includes determining abandwidth function that fits the plurality of wavelengths and theplurality of corresponding bandwidths, and determining a measured peakwavelength of the multi-mode optical fiber based on the bandwidthfunction. The measured peak wavelength maximizes the bandwidth function.The method further includes determining a difference between the targetpeak wavelength and the measured peak wavelength, and adjusting the atleast one drawing process parameter based on the difference between thetarget peak wavelength and the measured peak wavelength.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically depicts a multi-mode optical fiber manufacturingsystem according to one or more embodiments shown and described herein;

FIG. 2 schematically depicts bandwidth functions determined frommeasured bandwidth-wavelength pairs for four multi-mode optical fibersaccording to one or more embodiments shown and described herein;

FIG. 3 schematically depicts a function defining the relationshipbetween drawing tension and peak wavelength according to one or moreembodiments shown and described herein;

FIG. 4 schematically depicts a substantially real time peak wavelengthdetermination system according to one or more embodiments shown anddescribed herein;

FIG. 5 schematically depicts an exemplary multi-mode optical fiber peakwavelength determination system according to one or more embodimentsshown and described herein;

FIG. 6 schematically depicts a tunable light source including pluralityof programmable polarization controllers according to one or moreembodiments shown and described herein;

FIG. 7 schematically depicts a tunable light source including a singlepolarization controller according to one or more embodiments shown anddescribed herein;

FIG. 8 schematically depicts a tunable light source including a singletunable light emitter according to one or more embodiments shown anddescribed herein; and

DETAILED DESCRIPTION

Reference will now be made in detail to various embodiments for methodsfor modifying multi-mode optical fiber manufacturing processes, examplesof which are illustrated in the accompanying drawings. Wheneverpossible, the same reference numerals will be used throughout thedrawings to refer to the same or like parts. In one embodiment, a methodgenerally comprises measuring at least one characteristic of amulti-mode optical fiber. The at least one characteristic is a modalbandwidth or a differential mode delay. A measured peak wavelength ofthe multi-mode optical fiber is determined based on the measuredcharacteristic. A difference between the target peak wavelength and themeasured peak wavelength is determined. The process for manufacturingmulti-mode optical fiber is modified based on the difference between thetarget peak wavelength and the measured peak wavelength. The methods formodifying multi-mode optical fiber manufacturing processes will bedescribed in more detail herein with specific reference to the appendedfigures.

As used herein, the term “modal bandwidth” of a multi-mode optical fibermeans the frequency at which the amplitude of the optical output powerfrequency spectrum drops three decibels (3 dB) relative to the zerofrequency component of the fiber. Modal bandwidth is typically measuredin units of (frequency)*(distance) (e.g., MHz*km or GHz*km).Alternatively, modal bandwidth may be specified as a particularfrequency (e.g., in MHz or GHz) for a given length (e.g., in km).

As used herein, the term “peak wavelength” (also referred to as Lambda_Por λ₁) of a multi-mode optical fiber means a wavelength of light thatmaximizes a bandwidth of the multi-mode optical fiber. Techniques formeasuring the peak wavelength of a multi-mode optical fiber based onmulti-wavelength measurement techniques and differential mode delaytechniques will be described in detail below. Multi-mode optical fibermay be produced in order to have a bandwidth exceeding a bandwidththreshold at a target peak wavelength. In some embodiments, the targetpeak wavelength may be between 780 nm and 1650 nm. In some embodiments,the target peak wavelength is 850 nm. In some embodiments, the targetpeak wavelength is 980 nm or 1060 nm. In some embodiments, the targetpeak wavelength is between 1260 nm and 1360 nm, such as between 1300 nmand 1320 nm. However, it should be understood that multi-mode opticalfibers may be produced in order to have any target peak wavelength.

As used herein, the term “differential mode delay” of a multi-modeoptical fiber is the relative delay measured when varying the offset ofoutput pulses launched from a single-mode fiber at the input end of themulti-mode optical fiber. The detailed testing procedure for measuringdifferential mode delay is defined in TIA-455-220-A: FOTP-220Differential Mode Delay Measurement of Multimode Fiber in the TimeDomain.

As used herein, “drawing tension” is provided in units of grams (g).However, it should be understood that drawing tension measurementsprovided in grams may be converted to tension measurements in Newtons ordynes. To convert grams of drawing tension to Newtons of drawingtension, the drawing tension in grams is multiplied by 0.0098. Toconvert grams of drawing tension to dynes of drawing tension, thedrawing tension in grams is multiplied by 980.

Referring now to FIG. 1, one embodiment of a multi-mode optical fibermanufacturing system 100 for drawing multi-mode optical fiber 20 from amulti-mode optical fiber preform 112 is schematically depicted. Alsodepicted is a multi-mode optical fiber peak wavelength determinationsystem 160, which is operable to determine a measured peak wavelength ofa multi-mode optical test fiber 162 that is coupled to the multi-modeoptical fiber peak wavelength determination system 160. The measuredpeak wavelength determined by the multi-mode optical fiber peakwavelength determination system 160 may be used to modify the processfor manufacturing multi-mode optical fiber by the multi-mode opticalfiber manufacturing system 100 to enhance the performancecharacteristics of the drawn optical fiber, as will be described indetail below.

The multi-mode optical fiber preform 112 generally comprisessilica-based glass. In embodiments in which the multi-mode optical fiberpreform 112 comprises silica-based glass, the multi-mode optical fiberpreform 112 may include dopants that increase or decrease the refractiveindex of the silica-based glass relative to pure silica glass. In someembodiments, the multi-mode optical fiber preform 112 comprises a coresurrounded by cladding. In some embodiments, the multi-mode opticalfiber preform 112 comprises a doped or undoped glass core surrounded bya layer of doped or undoped glass. In some embodiments, the multi-modeoptical fiber preform 112 may be a core blank. In other embodiments, themulti-mode optical fiber preform 112 may be a cane formed from a coreblank, such as in embodiments in which the multi-mode optical fiberpreform 112 is one of a plurality of canes formed from a single coreblank.

In the embodiment depicted in FIG. 1, the multi-mode optical fibermanufacturing system 100 generally comprises a draw furnace 114, a fibercooling system 122, a coating system 130, a fiber take-up system 140,and a process controller 150.

The draw furnace 114 includes a heating element that supplies heat to atleast a bottom portion of the multi-mode optical fiber preform 112. Insome embodiments, the draw furnace may heat the bottom portion of themulti-mode optical fiber preform 112 to a draw temperature of about1700° C. to about 2100° C.

The multi-mode optical fiber 20 is drawn from the heated multi-modeoptical fiber preform 112 and through the various stages of themulti-mode optical fiber manufacturing system 100 with the fiber take-upsystem 140. The fiber take-up system 140 utilizes various drawingmechanisms 142 and pulleys 141 to provide the necessary tension to themulti-mode optical fiber 20 as the multi-mode optical fiber 20 is drawnthrough the multi-mode optical fiber manufacturing system 100, as willbe described in more detail below.

In the embodiment of the multi-mode optical fiber manufacturing system100 depicted in FIG. 1, the multi-mode optical fiber 20 is drawn fromthe multi-mode optical fiber preform 112 with the fiber take-up system140 and exits the draw furnace 114 along a substantially verticalpathway (i.e., a pathway along the z-direction). As the multi-modeoptical fiber is drawn along the vertical pathway, the multi-modeoptical fiber 20 may optionally be drawn through a fiber cooling system122 that cools the multi-mode optical fiber 20 prior to one or morecoatings being applied to the multi-mode optical fiber 20. The fibercooling system 122 is generally spaced apart from the draw furnace 114such that the multi-mode optical fiber 20 cools to temperaturessignificantly below the draw temperature before entering the fibercooling system 122. For example, the spacing between the draw furnace114 and the fiber cooling system 122 may be sufficient to cool themulti-mode optical fiber 20 from the draw temperature. While the fibercooling system 122 has been described herein as part of the multi-modeoptical fiber manufacturing system 100 for producing a multi-modeoptical fiber 20, it should be understood that the fiber cooling system122 is optional and that, in other embodiments, the multi-mode opticalfiber 20 may be drawn directly from the draw furnace 114 to a coatingsystem 130 without entering the fiber cooling system 122.

Still referring to FIG. 1, after the multi-mode optical fiber 20 exitsthe fiber cooling system 122, the multi-mode optical fiber 20 enters acoating system 130 where one or more coating layers are applied to themulti-mode optical fiber 20. In one embodiment described herein, thecoating system 130 applies at least one polymeric coating layer to themulti-mode optical fiber 20.

Still referring to FIG. 1, the process controller 150 may include aprocessor communicatively coupled to a memory. The memory containscomputer readable and executable instructions which are executed by theprocessor to control the process for manufacturing multi-mode opticalfiber and/or to modify the process for manufacturing multi-mode opticalfiber, as described herein. In some embodiments, the computer readableand executable instructions which are executed by the processor toadjust at least one drawing process parameter in order to modify theprocess for manufacturing multi-mode optical fiber, as will be describedin further detail below. In the embodiment depicted in FIG. 1, theprocess controller 150 is communicatively coupled to the draw furnace114 and the fiber take-up system 140 and may modify the process formanufacturing multi-mode optical fiber as described herein by modifyinga temperature of the draw furnace 114 and/or modifying the tensionapplied by the fiber take-up system 140, such as by adjusting a drawingspeed of the fiber take-up system 140. In some embodiments, the processcontroller 150 may only be communicatively coupled to one of the drawfurnace 114 and the fiber take-up system 140, such as in embodiments inwhich the process for manufacturing multi-mode optical fiber is adjustedby modifying only one of the temperature of the draw furnace 114 and thetension applied by the fiber take-up system 140.

As noted hereinabove, the multi-mode optical fiber peak wavelengthdetermination system 160 determines a measured peak wavelength of amulti-mode optical test fiber 162. The multi-mode optical fiber peakwavelength determination system 160 may include a processorcommunicatively coupled to a memory. The memory contains computerreadable and executable instructions which are executed by the processorto determine the measured peak wavelength of the multi-mode optical testfiber 162 based on at least one measured characteristic of themulti-mode optical test fiber 162, as will be described below.

In some embodiments, such as the embodiment depicted in FIG. 1, themulti-mode optical test fiber 162 may be provided for use in themulti-mode optical fiber peak wavelength determination system 160 byseparating a multi-mode optical fiber test segment from drawn multi-modeoptical fiber 20. The separated multi-mode optical fiber test segmentmay then be coupled to the multi-mode optical fiber peak wavelengthdetermination system 160 (e.g., via mechanical splicing or fusionsplicing) so that the measured peak wavelength of the separated fibermay be determined. In some embodiments, the multi-mode optical fibertest segment may be transferred to a spool before coupling themulti-mode optical fiber test segment to the multi-mode optical fiberpeak wavelength determination system 160. The multi-mode optical fibertest segment may be obtained at the initiation of the drawing process.In some embodiments, multiple multi-mode optical fiber test segments maybe separated and coupled to the multi-mode optical fiber peak wavelengthdetermination system 160, such as in embodiments in which fiber drawnduring a single process run is wound to multiple spools (e.g., using anindexing winder) and a multi-mode optical fiber test segment isseparated during a spool change. Furthermore, a multi-mode optical fibertest segment may be separated and coupled to the multi-mode opticalfiber peak wavelength determination system 160 at predefined intervals,such as once per 20 km, once per 30 km, once per 50 km, or at any otherinterval.

In other embodiments, the multi-mode optical fiber peak wavelengthdetermination system 160 may determine the measured peak wavelength ofthe drawn multi-mode optical fiber 20 before the fiber is separated fromthe multi-mode optical fiber perform 112. For example, in someembodiments, the multi-mode optical fiber peak wavelength determinationsystem 160 may determine the measured peak wavelength of the drawnmulti-mode optical fiber via an online peak wavelength measurementsystem that measures the peak wavelength of the drawn multi-mode opticalfiber 20 in real time as the fiber is drawn, as described below Such anonline measurement system allows the peak wavelength of the drawnmulti-mode optical fiber 20 to be measured and process parameters to beadjusted in substantially real time.

For example, one embodiment of a peak wavelength determination system400 in which the multi-mode optical fiber peak wavelength determinationsystem 160 determines the measured peak wavelength of the drawnmulti-mode optical fiber 20 substantially in real time as the multi-modeoptical fiber 20 is drawn is depicted in FIG. 4. In the peak wavelengthdetermination system 400 depicted in FIG. 4, the multi-mode opticalfiber 20 is drawn and wound into a coil 177 onto a support spool 176.The multi-mode optical fiber 20 is optically coupled to a first end 178a of a first test fiber 178. In some embodiments, the multi-mode opticalfiber 20 is optically coupled to the first end 178 a of the first testfiber 178 with a rotating optical coupler include in the support spool176, such as a fiber optic rotary joint (FORJ) device operable toconnect two fiber ends, allowing free rotation between them with minimaloptical signal loss. The rotating optical coupler allows the multi-modeoptical fiber 20 to remain in a relatively fixed position to allow foreffective coupling to the first test fiber 178.

Still referring to FIG. 4, a second end 178 b of the first test fiber178 is optically coupled to the multi-mode optical fiber peak wavelengthdetermination system 160, such as by a fiber coupler. The multi-modeoptical fiber peak wavelength determination system 160 is also opticallycoupled to the multi-mode optical fiber preform 112 by a second testfiber 179. Thus, the multi-mode optical fiber peak wavelengthdetermination system 160 effectively completes an optical loop formed bythe first test fiber 178, the multi-mode optical fiber 20, themulti-mode optical fiber perform 112, and the second test fiber 179.While the embodiment depicted in FIG. 4 includes the first test fiber178 and the second test fiber 179, it should be understood that someembodiments may not include the first test fiber 178 or the second testfiber 179, such as embodiments in which the multi-mode optical fiber 20and/or the multi-mode optical fiber perform 112 are directly coupled tothe multi-mode optical fiber peak wavelength determination system 160.

Still referring to FIG. 4, in operation, the multi-mode optical fiberpeak wavelength determination system 160 may launch light through oneend of the optical loop (either the first test fiber 178 or the secondtest fiber 179), receive the launched light through the other end of theoptical loop (either the second test fiber 179 or the first test fiber178), and determine the measured peak wavelength of the multi-modeoptical fiber 20 based on the received light based on differential modedelay measurements or multi-wavelength bandwidth determinationmeasurements, as will be described in detail below. Specifically, insome embodiments, the multi-mode optical fiber peak wavelengthdetermination system 160 may launch light into the first test fiber 178,which traverses through the multi-mode optical fiber 20, through themulti-mode optical fiber perform 112, through the second test fiber 179,and is received back at the multi-mode optical fiber peak wavelengthdetermination system 160, which then determines the measured peakwavelength of the multi-mode optical fiber 20 based on the receivedlight. In other embodiments, the multi-mode optical fiber peakwavelength determination system 160 may launch light into the secondtest fiber 179, which traverses through the multi-mode optical fiberperform 112, through the multi-mode optical fiber 20, through the firsttest fiber 178, and is received back at the multi-mode optical fiberpeak wavelength determination system 160, which then determines themeasured peak wavelength of the multi-mode optical fiber 20 based on thereceived light.

Accordingly, it should be understood that such a peak wavelengthdetermination system 400 may determine the measured peak wavelength ofthe drawn multi-mode optical fiber 20 substantially in real time as themulti-mode optical fiber 20 is drawn. It should also be understood thatthere are a variety of alternative systems and methods for determiningthe measured peak wavelength of the drawn multi-mode optical fiber 20substantially in real time other than the peak wavelength determinationsystem 400 shown in FIG. 4 and described above. For example, in someembodiments, light may be launched directly into the multi-mode opticalfiber perform 112, which travels through the multi-mode optical fiber20, through the first test fiber 178, and is received by the multi-modeoptical fiber peak wavelength determination system 160. In someembodiments, light may be launched at an angle into any of the firsttest fiber 178, the multi-mode optical fiber 20, the multi-mode opticalfiber perform 112, and the second test fiber 179. Furthermore, in someembodiments, the multi-mode optical fiber peak wavelength determinationsystem 160 may launch light into an end of the multi-mode optical fiber20 (either directly or via the first test fiber 178), which travelsthrough the multi-mode optical fiber perform 112, is incident upon areflector, and returns to the multi-mode optical fiber peak wavelengthdetermination system 160 along the same path.

Referring once again to FIG. 1, the multi-mode optical fiber peakwavelength determination system 160 is communicatively coupled to theprocess controller 150. However, in some embodiments, the multi-modeoptical fiber peak wavelength determination system 160 may not becommunicatively coupled to the process controller 150, such as inembodiments in which the multi-mode optical fiber peak wavelengthdetermination system 160 is separate from the multi-mode optical fibermanufacturing system 100, but at least one parameter of the multi-modeoptical fiber manufacturing system 100 is modified or adjusted based onthe peak wavelength of the multi-mode optical test fiber 162 asdetermined by the multi-mode optical fiber peak wavelength determinationsystem 160.

Having described the various components of the multi-mode optical fibermanufacturing system 100 and the interrelationship thereof, a method formodifying a process for manufacturing multi-mode optical fiber based ona measured peak wavelength will now be described.

A method for modifying a process for manufacturing multi-mode opticalfiber may include measuring at least one characteristic of a multi-modeoptical fiber and determining a measured peak wavelength of themulti-mode optical fiber based on the measured characteristic. Forexample, in some embodiments, a process for manufacturing multi-modeoptical fiber with the multi-mode optical fiber manufacturing system 100may be modified based on a peak wavelength of the multi-mode opticaltest fiber 162, as determined by the multi-mode optical fiber peakwavelength determination system 160. The multi-mode optical fiber peakwavelength determination system 160 may determine the measured peakwavelength of the multi-mode optical test fiber 162 in a variety ofways, two of which will be described in detail below.

1. Determining Measured Peak Wavelength Based on Multi-WavelengthMeasurement Techniques

In some embodiments, a modal bandwidth of the multi-mode optical testfiber 162 may be measured by the multi-mode optical fiber peakwavelength determination system 160 using a multi-wavelength measurementtechnique. The measured peak wavelength of the multi-mode optical testfiber 162 may be determined based on the measured modal bandwidth. Themulti-wavelength measurement technique may include emitting light at aplurality of wavelengths from at least one light source coupled to themulti-mode optical test fiber 162. The multi-mode optical fiber peakwavelength determination system 160 may then determine a plurality ofcorresponding modal bandwidths for light emitted at the plurality ofwavelengths. The multi-mode optical fiber peak wavelength determinationsystem 160 may then determine a bandwidth function that fits theplurality of wavelengths and the plurality of corresponding bandwidths,and determine the measured peak wavelength as the wavelength thatmaximizes the bandwidth function, as described in the followingparagraphs with reference to one embodiment of the multi-mode opticalfiber peak wavelength determination system 160 that is shown in FIG. 5.

FIG. 5 is a schematic diagram of an example multi-mode optical fiberpeak wavelength determination system 160. The multi-mode optical fiberpeak wavelength determination system 160 includes a tunable light source520, an optional polarization controller 540, an optical modulator 530,a mode conditioner 550, a photodetector 580, a network analyzer 600, acomputer 620, and a power supply 536.

Still referring to FIG. 5, the tunable light source 520 may beconfigured to emit light 522 having a select (central) wavelength λ anda narrow spectral width δλ. In one example, δλ≦0.1 nm or less, while inanother example δλ≦0.05 nm, while in yet another example, δ≦0.02 nm. Insome embodiments, the tunable light source 520 is tunable over awavelength range Δλ, which in various example Δλ≧50 nm, Δλ≧70 nm andΔλ≧80 nm. In an example, 50 nm≦Δλ≦150 nm. In some embodiments, thetunable light source 520 can generate light 522 at three wavelengths λ₁,λ₂ and λ₃ that in various examples are separated from each other by atleast 4 nm, or by at least 10 nm, or by at least 15 nm apart. In variousexamples, the tunable wavelength range can reside between thewavelengths of 800 nm and 1650 nm. Example wavelength ranges extend from790 to 880 nm or 990 nm to 1070 nm, or 1260 to 1360 nm, or 1400 nm to1550 nm, or 1500 nm to 1650 nm. In an example, the wavelength range Δλis 50 nm to 150 nm wide and resides within a wavelength window between750 nm and 1650 nm. In other examples, the wavelength window is 790 nmto 890 nm or 1260 nm to 1360 nm or 1450 nm to 1600 nm. Three exampleembodiments of the tunable light source 520 are described below.However, it should be understood that the tunable light source 520 maybe implemented in a manner other than specifically described herein.

Referring now to FIG. 6, another embodiment of a tunable light source isschematically depicted. Tunable light source 900 provides light sourcesat a plurality of wavelengths. The tunable light source 900 includes Nsingle-mode lasers, denoted 202-1, 202-2, . . . 202-i, 202-N that emitlight corresponding to wavelengths λ_(i), λ₂, . . . λ_(i), λ_(N),respectively. The N single-mode lasers are optically coupled to an N×1optical switch 220 via respective single-mode optical fiber sectionsF3-1, F3-2, . . . F3-i, F3-N. In some embodiments in which the opticalfiber sections F3 are not polarization maintaining, the tunable lightsource 900 may include a plurality of programmable polarizationcontrollers 210 arranged in each optical fiber section F3. In someembodiments, the N×1 optical switch 220 is programmable or may becontrolled by the computer 620. Programmable polarization controllers210 may be manual polarization controllers or may be controlled by thecomputer 620.

FIG. 7 schematically depicts a tunable light source 950. FIG. 7 issimilar to FIG. 6 and illustrates a tunable light source 950 in which asingle programmable polarization controller 210 is arranged between theN×1 optical switch 220 and the optical modulator 530. However, it shouldbe understood that in embodiments in which the optical fiber sections F1and F3 are polarization-maintaining, programmable polarizationcontroller 210 is not required.

FIG. 8 schematically depicts a tunable light source 970. FIG. 8 issimilar to FIG. 7 and illustrates an example embodiment in which thetunable light source 970 includes a single tunable light emitter 824. Insome embodiments, the single tunable light emitter 824 is asuperluminescent diode. In some embodiments, the superluminescent diodeemits light from about 825 nm to about 874 nm. In other embodiments, thesuperluminescent diode emits light from 793 nm to 880 nm. In otherembodiments, the single tunable light emitter 824 is a tunable laserthat emits light in the range from 1260 nm to 1360 nm.

Referring once again to FIG. 5, a first optical fiber section F1optically couples the tunable light source 520 to an input optical port532 a of the optical modulator 530. In some embodiments, the firstoptical fiber section F1 is polarization-maintaining with its state ofpolarization aligned such that no additional polarization management isneeded. In other embodiments in which the first optical fiber section F1is not polarization maintaining, a polarization controller 540 can beoperably arranged in the first optical fiber section between the tunablelight source 520 and the optical modulator 530. In some embodiments, theoptical modulator 530 is a lithium-niobate-based modulator. In someembodiments, the tunable light source 520 includes a pigtail fiber (notshown) that is optically coupled to the first optical fiber section F1.

Still referring to FIG. 5, the optical modulator 530 includes twoelectrical ports 534 a and 534 b. The two electrical ports 534 a and 534b are used to set a bias control voltage and provide RF driving signals,respectively. A power supply 536, which sets a DC voltage iselectrically connected to electrical port 534 a and a network analyzer600 is electrically connected to the electrical port 534 b.

Still referring to FIG. 5, the multi-mode optical fiber peak wavelengthdetermination system 160 further includes a mode conditioner 550optically coupled to the output end 532 b of the optical modulator 530via a second single-mode optical fiber section F2. In some embodiments,mode conditioner 550 may be a commercially available mode conditioner,such as the ModCon mode controller sold by Arden Photonics, Ltd., WestMidland, United Kingdom. In some embodiments, the mode conditioner 550may employ a multimode fiber (e.g., 50 micron core radius) and generatesa Gaussian light intensity profile radially across the multimode fibercore and may provide a launch condition similar to the launch conditionof a VCSEL. In other embodiments, the mode conditioner 550 may be acustomized device that is designed to provide the launch conditions forvarious type of lasers and optics.

Still referring to FIG. 5, the mode conditioner 550 in turn is opticallycoupled to an input end of a multi-mode optical test fiber 162 whosemeasured peak wavelength is to be determined. In an example, themulti-mode optical test fiber 162 has a select length, e.g., 1 km ormany other lengths of choices, such as 100 m, 300 m, 2.2 km, 5.6 km, 8.8km or even 16.5 km. Thus, in an example, the multi-mode optical testfiber 162 has a length in the range from 100 m to 16.5 km.

Still referring to FIG. 5, the multi-mode optical test fiber 162includes an output end that is optically coupled to a photodetector 580.The photodetector 580 is electrically connected to the network analyzer600 and generates detector signals SD, which are received and analyzedby the network analyzer 600. In some embodiments, the photodetector 580includes an internal linear amplifier (not shown) to boost the strengthof detector signals SD. In other embodiments, such as the embodimentdepicted in FIG. 5, an external linear amplifier 582 disposed betweenthe photodetector 580 and the network analyzer 600 is also used tofurther boost the strength of detector signals SD.

Still referring to FIG. 5, the multi-mode optical fiber peak wavelengthdetermination system 160 also includes a computer 620 that iselectrically connected to the tunable light source 520, the networkanalyzer 600, and the power supply 536. The computer 620 includes adisplay 621. In an example, the computer 620 comprises a computer orlike machine that is adapted (e.g., via instructions such as softwareembodied in a computer-readable or machine-readable medium) to cause thecomputer to control the operation of the various components of themulti-mode optical fiber peak wavelength determination system 160. Thecomputer 620 includes a processor unit (“processor”) 622 and a memoryunit (“memory”) 624. An example computer 620 is or includes a computerwith a processor and includes an operating system such as MicrosoftWINDOWS or LINUX or Apple's OS X. The processor 622 may include anyprocessor or device capable of executing a series of softwareinstructions and includes, without limitation, a general-purpose orspecial-purpose microprocessor, finite state machine, computer,computer, central-processing unit (CPU), field-programmable gate array(FPGA) or digital signal processor. The memory 624 is operably connectedto the processor 622. As used herein, the term “memory” refers to anyprocessor-readable medium, including but not limited to RAM, ROM, EPROM,PROM, EEPROM, disk, floppy disk, hard disk, CD-ROM, DVD or the like, onwhich may be stored a series of instructions executable by the processor622.

Still referring to FIG. 5, the peak wavelength measurement methodsdescribed herein may be implemented in various embodiments in amachine-readable medium (e.g., the memory 624) comprising machinereadable instructions (e.g., computer programs and/or software modules)for causing the computer 620 to perform the measurement methodsdescribed herein by controlling the operation of the multi-mode opticalfiber peak wavelength determination system 160. In some embodiments, thecomputer programs may be executed by the processor 622 from the memory624. The computer programs and/or software modules may comprise multiplemodules or objects in order to perform the various methods of thepresent disclosure and to control the operation and function of thevarious components of the multi-mode optical fiber peak wavelengthdetermination system 160. The type of computer programming languagesused for the code may range from procedural code-type languages toobject-oriented languages. The files or objects need not have aone-to-one correspondence to the modules or method steps described.Further, the method and system may comprise combinations of software,hardware and firmware. Firmware can be downloaded into the processor 622for implementing the various example embodiments disclosed herein.

In an example of the operation of the multi-mode optical fiber peakwavelength determination system 160 depicted in FIG. 5, the computer 620may cause a control signal S0 to be sent to the tunable light source520, which causes the tunable light source 520 to emit light 522 havinga first wavelength λ₁. In another example, the tunable light source 520is controlled manually rather than via the computer 620. In one exampleembodiment, the first wavelength λ₁ can be about 807 nm, whilesubsequent wavelengths λ₂ and λ₃ can be about 850 nm and 894 nm,respectively.

Still referring to FIG. 5, the light 522 travels through the opticalmodulator 530, which is electrically controlled by the computer 620 viathe power supply 536 and by the network analyzer 600. The computer 620may control the optical modulator 530 by controlling a bias controlvoltage set by the power supply 536 via a control signal S1 a from thecomputer 620. The bias voltage can be wavelength dependent, in whichcase it may be set for the optimal value for each wavelength. Theoptimal bias voltage may be determined beforehand and input into thecomputer 620. The computer 620 can then control the power supply 536 todeliver the proper bias voltage through the use of a standard controlinterface, such as GPIB, USB, RS-232, or Ethernet. Alternatively, anautomatic bias control circuit (not shown) may be employed to set thebias voltage automatically by monitoring the input and output light astapped from a couple fiber splitters (not shown).

Still referring to FIG. 5, the network analyzer 600 may control theoptical modulator 530 by providing a frequency control signal S1 b(e.g., a RF drive signal) to the optical modulator 530 to sweep themodulation frequency over a select range frequency range Δf=f_(H)−f_(L)where f_(H) is the highest frequency in the range and f_(L) is thelowest frequency in the range. In some embodiments, the lowest frequencyf_(L) of frequency range Δf is 10 Khz or 100 KHz or 500 KHz or 1 MHz or5 MHz or 10 MHz or 200 Mhz or any number in between. In someembodiments, the highest frequency f_(H) of frequency range Δf is 100MHz, or 500 MHz, or 1 GHz, or 10 GHz or 20 GHz or 40 GHz or 60 GHz orany number in between.

Thus, control signals S1 a and S1 b from the computer 620 and thenetwork analyzer 600 are used to control the optical modulator 530 sothat the optical modulator 530 converts the light 522 into modulatedlight 522M. The modulated light 522M then passes through the fibersection F2 and then through the mode conditioner 550. The modeconditioner 550 is configured to recondition the modulated light 522Mfrom its single-mode light distribution into a multi-mode lightdistribution suitable for launching into the multi-mode optical testfiber 162. Thus, the modulated light 522M exits the mode conditioner 550and enters the input end the multi-mode optical test fiber 162 asmode-conditioned modulated light 522MC.

Still referring to FIG. 5, the mode-conditioned modulated light 522MCtravels through the multi-mode optical test fiber 162 as a guided wavethat travels in the multiple modes, and then exits the multi-modeoptical test fiber 162 at the output end. The light output from themulti-mode optical test fiber 162 is then detected by the photodetector580. The photodetector 580 receives and converts the light output by themulti-mode optical test fiber 162 to detector signal SD. In an example,detector signal SD is amplified either within the photodetector 580 orby the external linear amplifier 582. The detector signal SD is thenreceived and analyzed by the network analyzer 600, which analyzes thedetector signal SD.

Still referring to FIG. 5, the multi-mode optical fiber peak wavelengthdetermination system 160 may determine a bandwidth of the multi-modeoptical test fiber 162 based on the detector signal SD received by thenetwork analyzer 600 that corresponds to the wavelength of light emittedby the tunable light source 520. In some embodiments, the bandwidth ofthe multi-mode optical test fiber 162 at the wavelength emitted by thetunable light source 520 may be determined by: determining the opticaltransfer function of the multi-mode optical test fiber 162 (which mayneed to be adjusted or calibrated based on the set-up of the multi-modeoptical fiber peak wavelength determination system 160) and determiningthe bandwidth based on the optical transfer function (e.g., thefrequency at the 3 optical dB or 6 electric dB below the signal level atthe zero modulation frequency). The bandwidth of the multi-mode opticaltest fiber 162 is determined in this manner for light emitted at each ofa plurality of wavelengths. For example, a first bandwidth BW1 of themulti-mode optical test fiber 162 may be determined for light emitted ata first wavelength λ₁. Then, a second bandwidth BW2 of the multi-modeoptical test fiber 162 may be determined for light emitted at a secondwavelength λ. Then, a third bandwidth BW3 of the multi-mode optical testfiber 162 may be determined for light emitted at a third wavelength λ₃.Once the bandwidths are determined at each desired wavelength, abandwidth function is determined that fits the plurality of wavelengthsand the plurality of corresponding bandwidths. In some embodiments, thebandwidth function may be derived from a Gaussian model for a multimodeoptical fiber. The measured peak wavelength of the multi-mode opticaltest fiber 162 is then determined from the bandwidth function as thewavelength that maximizes the bandwidth function.

Thus, it should be understood that multi-mode optical fiber peakwavelength determination system 160 depicted in FIG. 5 and describedabove is operable to emit light at a plurality of wavelengths from atleast one light source coupled to the multi-mode optical test fiber 162,determine a plurality of corresponding modal bandwidths for lightemitted at the plurality of wavelengths, determine a bandwidth functionthat fits the plurality of wavelengths and the plurality ofcorresponding bandwidths, and then determine the measured peakwavelength of the multi-mode optical test fiber 162 as the wavelengththat maximizes the bandwidth function.

2. Determining Measured Peak Wavelength Based on Differential Mode DelayMeasurement

In some embodiments, differential mode delay data may be measured forthe multi-mode optical test fiber 162 by the multi-mode optical fiberpeak wavelength determination system 160 and the measured peakwavelength of the multi-mode optical test fiber 162 may be determinedbased on the measured differential mode delay data. For example, adifferential mode delay test may be performed on the multi-mode opticaltest fiber 162 and raw differential mode delay data may be obtained. Theraw differential mode delay data may include the measured intensity ofthe optical pulse at a range of radial offsets from the centerline ofthe multi-mode optical test fiber 162. From the raw differential modedelay data, the RMS center (which may be referred to as the “DMDcentroid” or D) of the optical pulse may be further calculated at eachradial offset r, to generate a plurality of (D, r) pairs. The (D,r)pairs may be fitted to a function of the form D=a+DMD_(slope)*(r/R)²,where a and DMD_(slope) are constants and R is the maximal radial offsetfor which differential mode delay data was obtained. Using a leastsquares weighted method, the values of a and DMA_(slope) may bedetermined through a best fitting procedure. From the determined valuefor DMD_(slope), the measured peak wavelength may be determinedaccording to the following equation:λ_(p, measured)=850−DMA_(lope)*255.0. For example, FIG. 9 depicts a plotof actual DMD centroid data along with the best fit DMD centroid line tofir the actual DMD centroid data. From the best fit DMD centroid line, ais determined to be 0.0276 and DMD_(slope) is determined to be −0.142.From these parameters, the measured peak wavelength is determined to beλ_(p, measured)=850−DMD_(slope)*255.0=850−(−0.142)*255.0=886.21 nm.While the equations above are applicable for a multimode optical fiberwith a peak wavelength within 100 nm of 850 nm (e.g., with a peakwavelength between 750 nm and 950 nm), it should be understood thatsimilar equations may be derived for multimode optical fibers with apeak wavelength other than 850 nm.

Once the measured peak wavelength of the multi-mode optical test fiber162 is determined with the multi-mode optical fiber peak wavelengthdetermination system 160, a difference between the target peakwavelength and the measured peak wavelength is determined. For example,the difference Δλ_(p) may be determined asΔλ_(p)=λ_(p, target)−λ_(p, measured).

The process for manufacturing multi-mode optical fiber is then modifiedbased on the difference between the target peak wavelength and themeasured peak wavelength. In some embodiments, the process formanufacturing multi-mode optical fiber is modified by adjusting at leastone drawing process parameter. The adjusted drawing process parametermay include a temperature of a drawing furnace, a drawing speed of themulti-mode optical fiber, or a mechanically applied drawing tension ofthe multi-mode optical fiber.

The process for manufacturing multi-mode optical fiber may be modifiedin order to achieve a desired drawing tension associated with a targetpeak bandwidth. For example, in some embodiments, the process formanufacturing multi-mode optical fiber is modified by adjusting adrawing tension according to the following equation: Δλ_(p)=c*Δλ_(g),wherein Δλ_(g) is a drawing tension adjustment amount and Δλ_(p) is thedifference between the target peak wavelength and the measured peakwavelength. The drawing tension adjustment may be effectuated byadjusting the temperature of the draw furnace 114 or adjusting thedrawing speed of the fiber take-up system 140. Typically, an increase inthe temperature of the draw furnace 114 will cause a decrease in drawingtension and a decrease in the temperature of the draw furnace 114 willcause an increase in drawing tension. Generally, an increase in thedrawing speed of the fiber take-up system 140 will cause an increase indrawing tension and a decrease in the drawing speed of the fiber take-upsystem 140 will cause a decrease in drawing tension.

In some embodiments, the process for manufacturing multi-mode opticalfiber is modified when the difference between the target peak wavelengthand the measured peak wavelength exceeds a threshold. In one embodiment,the process for manufacturing multi-mode optical fiber is modified byhalting the process for manufacturing multi-mode optical fiber when thedifference between the target peak wavelength and the measured peakwavelength exceeds a threshold. For example, in one embodiment, amulti-mode optical fiber may be required to meet a bandwidth requirementat a particular wavelength (e.g., 850 nm) in order to be characterizedas fiber of a particular quality grade (e.g., OM4 fiber). In otherembodiments, a multi-mode optical fiber may be required to have abandwidth above a threshold (e.g., 500 MHz*km) with an overfilled launchcondition at 1300 nm in order to be characterized as a passing fiber.When the difference between the target peak wavelength and the measuredpeak wavelength exceeds a determined threshold, a determination may bemade that the fiber will not satisfy the bandwidth requirement andproduction of the fiber may be halted, thereby reducing the wasteresulting from producing failing fiber.

In some embodiments, the process for manufacturing multi-mode opticalfiber may be halted and the process for manufacturing multi-mode opticalfiber may be restarted after the process for manufacturing multi-modeoptical fiber is modified. For example, in some embodiments, amulti-mode optical fiber test segment may be separated from drawnmulti-mode optical fiber 20. The separated multi-mode optical fiber testsegment may then be coupled to the multi-mode optical fiber peakwavelength determination system 160 (e.g., via mechanical splicing orfusion splicing) so that the peak wavelength of the separated fiber maybe determined. Once the measured peak wavelength of the separated fiberis determined, a difference between the target peak wavelength and themeasured peak wavelength may be determined, the process may be modifiedbased on the difference (e.g., by adjusting the tension), and theprocess may be restarted after the process is modified.

In some embodiments, a core blank may be formed. A plurality of corecanes (e.g., four) may be drawn from the core blank. The core canesdrawn from the same core blank, sometimes referred to as “sister canes”typically share similar physical properties. The plurality of core canesmay be further processed to form respective preforms for drawing intomultimode fibers (e.g., a first core cane preform, a second core canepreform, etc.). The multi-mode optical fiber may be drawn from a firstcore cane preform, the drawing process may be modified based on ameasured peak wavelength of the fiber drawn from the first core canepreform, and additional multi-mode optical fiber may be drawn from asecond core cane preform after the process for manufacturing multi-modeoptical fiber is modified so that fiber drawn from the second core canepreform will have a peak wavelength (and resultant performancecharacteristics) closer to the target peak wavelength (and resultantperformance characteristics). For example, a core blank may be separatedinto four core canes, which are further processed to form respectivecore cane preforms for drawing into multimode fibers (e.g., a first corecane preform, a second core cane preform, a third core cane preform, anda fourth core cane preform). A first multi-mode optical fiber may bedrawn from the first core cane preform. The first multi-mode opticalfiber drawn from the first core cane preform may then be coupled to themulti-mode optical fiber peak wavelength determination system 160. Themeasured peak wavelength of the first multi-mode optical fiber may bedetermined by the multi-mode optical fiber peak wavelength determinationsystem 160 (e.g., by using the multi-wavelength measurement techniquesor differential mode delay techniques described in detail hereinabove).At least one drawing process parameter (e.g., the temperature of thedraw furnace 114, the drawing speed of the fiber take-up system 140, thedrawing tension, or the like) may be adjusted based on a differencebetween the target peak wavelength and the measured peak wavelength andfiber may be drawn from one or more additional core cane preforms (e.g.,the sister core canes of the first core cane) using the adjusted drawingtension.

It should be understood that the methods described herein may modifymulti-mode optical fiber manufacturing processes based on measured peakwavelength in order to produce multi-mode optical fiber havingconsistent performance characteristics at or above a desired level. Forexample, the methods described herein may modify multi-mode opticalfiber manufacturing processes based on a difference between a targetpeak wavelength and a measured peak wavelength by adjusting drawingtension in a manner that produces fiber closer to the target peakwavelength, thereby possessing enhanced bandwidth characteristics. Suchmanufacturing processes may avoid wasted fiber and avoid producing lowquality fiber.

The following examples will aid in further understanding the claimedsubject matter. However, it should be understood that the claimedsubject matter is not limited in any way by the following examples.

Example 1

In one example, a number of multi-mode optical fibers were drawn atdifferent drawing tensions, the measured peak wavelength of each of thefour drawn multi-mode optical fibers was determined, a function definingthe relationship between drawing tension and peak wavelength wasestablished, the measured peak wavelength of a test segment of drawnfiber was determined, a difference between a target peak wavelength andthe measured peak wavelength of the test segment was determined, and theprocess for manufacturing multi-mode optical fiber was modified based onthe difference between the target peak wavelength and the measured peakwavelength, as will be described in further detail below.

As noted above, in this example, a number of multi-mode optical fiberswere drawn at different drawing tensions. Four multi-mode optical fiberswere drawn at a draw speed of about 70 meters per minute. The drawingtension of each of the four multi-mode optical fibers was adjusted byadjusting the temperature of the drawing furnace. Specifically, thefirst multi-mode optical fiber was drawn at a tension of 54 g(corresponding to a drawing furnace temperature of 2080° C.), the secondmulti-mode optical fiber was drawn at a tension of 63 g (correspondingto a drawing furnace temperature of 2030° C.), the third multi-modeoptical fiber was drawn at a tension of 89 g (corresponding to a drawingfurnace temperature of 1980° C.), and the fourth multi-mode opticalfiber was drawn at a tension of 147 g (corresponding to a drawingfurnace temperature of 1930° C.). Each time the tension was adjusted byadjusting the temperature of the drawing furnace, the root was slightlyaltered, resulting in a drawing speed change. After about 2-3 minutes,the drawing speed stabilized at about 70 meters per minute. After thedrawing speed stabilized, about 500 meters of multi-mode fiber weredrawn and separated for coupling to the multi-mode optical fiber peakwavelength determination system 160.

The measured peak wavelength of each of the four drawn multi-modeoptical fibers was determined by the multi-mode optical fiber peakwavelength determination system 160. Specifically, light emitted at aplurality of wavelengths (807 nm, 850 nm, and 894 nm) was coupled intoeach of the multi-mode optical fibers and a bandwidth of each fiber wasdetermined at each wavelength. From the bandwidth-wavelength pairs foreach of the four fibers, four separate bandwidth functions weredetermined that fit the bandwidth-wavelength pairs, as illustrated inFIG. 2. The measured peak wavelength of each of the four fibers wasdetermined as the wavelength that maximized the corresponding bandwidthfunction illustrated in FIG. 2. The measured peak wavelength of thefiber drawn at 147 g was determined to be 731.9 nm. The measured peakwavelength of the fiber drawn at 89 g was determined to be 782.49 nm.The measured peak wavelength for the fiber drawn at 63 g was determinedto be 854.95 nm. The measured peak wavelength for the fiber drawn at 54g was determined to be 861.6 nm.

Once the measured peak wavelength of each of the four fibers wasdetermined, a function defining the relationship between drawing tensionand peak wavelength was established by fitting the measured peakwavelength and drawing tension data for each of the four fibers, asillustrated in FIG. 3. For example, the fitted line of FIG. 3 may bedescribed by the equation λ_(p)=c*T_(g)+d, where T_(g) is a drawingtension and is the peak wavelength, c is about −1.43, and d is about33.69. While the peak wavelength to tension relationship depicted inFIG. 3 is a fitted line, it should be understood that in otherembodiments, the relationship between the peak wavelength and drawingtension may not be a linear function, such as in embodiments in whichthe peak wavelength and drawing tension are related by a non-linearfunction or a look-up table. Furthermore, it should be understood that afunction or relationship may be defined to relate peak wavelength to thetemperature of the drawing furnace or any other process parameter thatdirectly or indirectly influences drawing tension. Moreover, it shouldbe understood that the particular relationship between drawing tensionand peak wavelength may vary based on characteristics of the preform,the components of the drawing system, ambient conditions, drawingprocess parameters, and the like, but the particular relationshipbetween drawing tension and peak wavelength may be determined in themanner described hereinabove for any set of conditions.

Once a relationship was established between the drawing tension and thepeak wavelength (in this particular case λ_(p)=−1.43*T_(g)+d), themeasured peak wavelength of a test segment of drawn fiber wasdetermined, a difference between the target peak wavelength and themeasured peak wavelength of the test segment was determined, and theprocess for manufacturing multi-mode optical fiber was modified based onthe difference between the target peak wavelength and the measured peakwavelength by modifying the drawing tension based on the relationshipbetween the drawing tension and the peak wavelength. Specifically, asample of fiber was drawn and separated for coupling to the multi-modeoptical fiber peak wavelength determination system 160. The peakwavelength of the sample fiber was determined by the multi-mode opticalfiber peak wavelength determination system 160 to be 820 nm. The targetpeak wavelength for the fiber was 850 nm. Thus, the difference betweenthe target peak wavelength of the test segment and the measured peakwavelength (Δλ_(p)) is 30 nm, corresponding to a 21 g decrease indrawing tension to achieve the target peak wavelength of 850 nm(Δλ_(p)=−1.43*Δλ_(g)). The process for manufacturing the multi-modeoptical fiber was modified by increasing the temperature of the drawfurnace to an amount sufficient to decrease the drawing tension by 21 gwhile maintaining the same draw speed, fiber diameter. In otherembodiments, the tension may be adjusted by adjusting one or moreparameters of the fiber take-up system 140. Furthermore, it should beunderstood that the drawing tension may be adjusted by the processcontroller 150 receiving a desired tension set-point input by a user ofcontrol software, which may cause the process controller 150 to alterfiber manufacturing parameters in order to achieve the desired tensionset-point.

Example 2

In another example, a number of optical fibers were drawn to have peakwavelengths at several target peak wavelengths. The modal bandwidth ofeach of the fibers was measured using a ModCon multimode fiberconditioner, commercially available from Ardent, which creates a typicalmultimode fiber launch condition as typically seen in VCSEL-based lasersources. To evaluate the ability to achieve various target peakwavelengths, drawing tensions were adjusted based on a function thatdefines the relationship between the change in drawing tension and thechange in peak wavelength. The function defining the relationshipbetween the change in drawing tension and change in peak wavelength maybe any of the functions described above, or any other mathematical orempirical relation that maps target peak wavelength to drawing tension.The peak wavelength of each of the fibers was then measured to determinehow close the measured peak wavelength was to the target peakwavelength. Specifically, a first fiber was drawn at a tension of 125 g.The peak wavelength of the first fiber was measured to be 852 nm. Thepeak bandwidth of the first fiber was 8.82 GHz*km and the bandwidth ofthe first fiber at 850 nm was 8.79 GHz*km. A second fiber was drawn fromthe same preform as the first fiber at a tension of 155 g, which was thedrawing tension determined to correspond to a target peak wavelength of809 nm based on the function. The peak wavelength of the second fiberwas measured to be 816 nm, which is within 7 nm of the 809 nm targetpeak wavelength. The peak bandwidth of the second fiber was 7.51 GHz*kmand the bandwidth of the second fiber at 850 nm was 3.95 GHz*km.Subsequently, a third fiber was drawn from the same preform at a tensionof 136 g, which was the drawing tension determined to correspond to atarget peak wavelength of 837 nm based on the function. The peakwavelength of the third fiber was measured to be 837 nm, which is thesame as the target peak wavelength. The peak bandwidth of the thirdfiber was 7.46 GHz*km and the bandwidth of the third fiber at 850 nm was6.83 GHz*km.

Example 3

In another example using another preform, a fiber was drawn at aspecified drawing tension of 147 g. After 20 km of the fiber was drawn,a first 1 km fiber sample was taken and the peak wavelength was measuredto be 848 nm with peak bandwidth of 7.18 GHz*km and bandwidth at 850 nmto be 7.16 GHz*km. The draw tension was reduced by 17 g tension (to 130g), resulting in a target peak wavelength of 873 nm. The peak wavelengthof the fiber was measured to be 871 nm for a second 1 km sample afterthe adjustment in the tension. The measured peak wavelength of 871 nm iswithin 2 nm of the target peak wavelength, demonstrating the ability totightly control peak wavelength. The peak bandwidth of the second fibersample was 8.13 GHz*km with a bandwidth at 850 nm of 6.62 GHz*km. Thedraw tension was then increased by 14 g (to 144 g), resulting in atarget peak wavelength of 850 nm. After waiting a few minutes to allowthe tension to stabilize, a third 1 km sample fiber was taken, the peakwavelength of which was measured to be 850 nm. The fact that themeasured peak wavelength of the third fiber was the same as the targetpeak wavelength further demonstrates the ability to tightly control peakwavelength in manufactured multi-mode optical fiber.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the embodiments describedherein without departing from the spirit and scope of the claimedsubject matter. Thus it is intended that the specification cover themodifications and variations of the various embodiments described hereinprovided such modification and variations come within the scope of theappended claims and their equivalents.

What is claimed is:
 1. A method for modifying a process formanufacturing multi-mode optical fiber, the method comprising: measuringat least one characteristic of a multi-mode optical fiber, wherein theat least one characteristic is a modal bandwidth or a differential modedelay at one or more wavelengths; determining a measured peak wavelengthof the multi-mode optical fiber based on the measured characteristic;determining a difference between a target peak wavelength and themeasured peak wavelength; and modifying the process for manufacturingmulti-mode optical fiber based on the difference between the target peakwavelength and the measured peak wavelength.
 2. The method of claim 1,wherein the at least one characteristic is the modal bandwidth and themethod further comprises: coupling light emitted at a plurality ofwavelengths from at least one light source into the multi-mode opticalfiber; determining a plurality of corresponding bandwidths for lightemitted at the plurality of wavelengths, wherein each wavelength isassociated with a corresponding bandwidth; and determining a bandwidthfunction that fits the plurality of wavelengths and the plurality ofcorresponding bandwidths, wherein the measured peak wavelength maximizesthe bandwidth function.
 3. The method of claim 1, wherein the processfor manufacturing multi-mode optical fiber is modified by adjusting atleast one drawing process parameter.
 4. The method of claim 3, whereinthe at least one drawing process parameter includes a temperature of adrawing furnace, a drawing speed of the multi-mode optical fiber, or amechanically applied drawing tension of the multi-mode optical fiber. 5.The method of claim 3, wherein the process for manufacturing multi-modeoptical fiber is modified by adjusting a drawing tension as a functionof the difference between the target peak wavelength and the measuredpeak wavelength.
 6. The method of claim 5, wherein the process formanufacturing multi-mode optical fiber is modified by adjusting thedrawing tension according to the following equation: Δλ_(p)=c*Δλ_(g),wherein Δλ_(g) is a drawing tension adjustment amount from a previousdrawing tension and Δλ_(p) is the resulting difference of peakwavelength between the target peak wavelength and the measured peakwavelength.
 7. The method of claim 1, wherein the process formanufacturing multi-mode optical fiber is modified when the differencebetween the target peak wavelength and the measured peak wavelengthexceeds a threshold.
 8. The method of claim 7, wherein the process formanufacturing multi-mode optical fiber is modified by halting theprocess for manufacturing multi-mode optical fiber when the differencebetween the target peak wavelength and the measured peak wavelengthexceeds the threshold.
 9. The method of claim 1, further comprisingseparating a multi-mode optical fiber test segment from a drawnmulti-mode optical fiber, wherein the measured characteristic is acharacteristic of the multi-mode optical fiber test segment.
 10. Themethod of claim 9, further comprising coupling the multi-mode opticalfiber test segment to a peak wavelength determination system thatdetermines the measured peak wavelength.
 11. The method of claim 10,further comprising transferring the multi-mode optical fiber testsegment to a spool before coupling the multi-mode optical fiber testsegment to the peak wavelength determination system.
 12. The method ofclaim 1, further comprising halting the process for manufacturingmulti-mode optical fiber and restarting the process for manufacturingmulti-mode optical fiber after the process for manufacturing multi-modeoptical fiber is modified.
 13. The method of claim 1, furthercomprising: drawing the multi-mode optical fiber from a first preformformed from a first cane of a core blank; and drawing additionalmulti-mode optical fiber from a second preform formed from a second caneof the core blank after the process for manufacturing multi-mode opticalfiber is modified.
 14. The method of claim 1, wherein the target peakwavelength is between 780 nm and 1650 nm.
 15. A method for adjusting atleast one drawing process parameter in a process for manufacturingmulti-mode optical fiber, the method comprising: coupling light emittedfrom at least one light source at a plurality of wavelengths into amulti-mode optical fiber; determining a plurality of correspondingbandwidths for light emitted at the plurality of wavelengths, whereineach wavelength is associated with a corresponding bandwidth;determining a bandwidth function that fits the plurality of wavelengthsand the plurality of corresponding bandwidths; determining a measuredpeak wavelength of the multi-mode optical fiber based on the bandwidthfunction, wherein the measured peak wavelength maximizes the bandwidthfunction; determining a difference between a target peak wavelength andthe measured peak wavelength; and adjusting the at least one drawingprocess parameter based on the difference between the target peakwavelength and the measured peak wavelength.
 16. The method of claim 15,wherein the at least one drawing process parameter includes atemperature of a drawing furnace, a drawing speed of the multi-modeoptical fiber, or a mechanically applied drawing tension of themulti-mode optical fiber.
 17. The method of claim 15, wherein theprocess for manufacturing multi-mode optical fiber is modified byadjusting a drawing tension as a function of the difference between thetarget peak wavelength and the measured peak wavelength.
 18. The methodof claim 15, wherein the process for manufacturing multi-mode opticalfiber is modified by adjusting the drawing tension according to thefollowing equation: Δλ_(p)=c*Δλ_(g), wherein Δλ_(g) is a drawing tensionadjustment amount from a previous drawing tension and A λ_(p) is theresulting difference of peak wavelength between the target peakwavelength and the measured peak wavelength.
 19. The method of claim 15,wherein the at least one drawing process parameter is adjusted when thedifference between the target peak wavelength and the measured peakwavelength exceeds a threshold.
 20. The method of claim 15, furthercomprising: drawing the multi-mode optical fiber from a first preformformed from a first cane of a core blank; and drawing additionalmulti-mode optical fiber from a second preform formed from a second caneof the core blank after the process for manufacturing multi-mode opticalfiber is modified.